A review of the UK fast reactor programme, March 1981

A reduction in electricity sales over the last year had led to some fossil-fuelled stations being prematurely retired and has postponed the start of some new stations. Nevertheless the main programme for the building of 1 5 G We of thermal reactors during the next ten years remains unaltered and as summarised in last year's review. A formal request to build the first PWR at Sizewell in Suffolk has been presented by the CEGB to the government. This is expected to lead to a Public Inquiry within the next 12-18 months. The major contracts for building the AGR stations at Torness and Heysham were placed recently. Reduced projections for electricity demand up to the end of the century have also contributed to a delay in the government's response to the recommendation by the industry that the Commercial Demonstration Fast Reactor (CDFR) should be built to ensure that the option for commercial LMFBR should be demonstrated and maintained. A government statement is now expected before the end of 1981. Fast breeder reactors are expected to be required in the UK electrical supply system by about the turn of the century. Series ordering will be preceded by construction and operation of the CDFR, of a design suitable in all basic features for replication in programme reactors. The National Nuclear Corporation (NNC) has continued the development of a CDFR design having the required operational safety and economic characteristics. The basic design concept is now nearing completion following investigation of a number of alternatives. Some of the more important features of this design, namely the core, primary circuit and reactor cooling systems. steam cycle and boilers, and overall plant and station layout are described in this review. As a result of increased understanding of sodium/water reaction behaviour, development of manufacturing and inspection techniques and experience in plugging and repair of tubes containing leaking welds, coupled with the preference for a once through steam cycle, a re-evaluation of various boiler design styles have been undertaken. The types being studied cover straight tube, U and J tube, hockey stick and helical coil designs. A final choice of steam generator for CDFR has not yet been made. Key features in design selection are overall integrity to ensure high availability, ease of maintenance and repair following minor tube leaks, resistance to escalation of minor leaks to more major sodium/water reaction incidents. inspectability, relevance of previous experience and capital cost. Operation of the PFR was interrupted by a series of small leaks in the tube-to-tube plate welds in the three evaporator units. The key areas have now been shot-peened to remove tensile stresses in the surface material. the units have been repaired and operation at high power should be restarted during March 1981. The performance of the core and primary circuits has continued to be excellent. A major step forward was taken when the first 16 sub-assemblies were reprocessed in the PFR reprocessing plant. During the year a system economic study has been completed to assist in providing a sound technical basis for a fast reactor inquiry. This study was based on a set of programme assumptions and economic ground rules developed and agreed in 1978 within the UK nuclear industry and updated in 1979. Broadly, it was concluded that the introduction of the fast reactor as soon and as rapidly as feasible also leads, even on conservative uranium price assumptions. to economic benefits, the benefits being greatest when electrical demand and raw fuel prices are at their highest. The benefits are little affected by 25% increases in costs, except for an increase in fast reactor capital cost when uranium stays cheap; in this case the benefit virtually disappears if it is assumed that all other capital costs stay constant. Use of the fast reactor also produces a dramatic fall (almost three-fold) in the need uranium imports and, if market forces are allowed plausible influence on the assumed uranium price, the cost benefit increases several fold. It is advantageous to return discharged fast reactor fuel to the reactor as rapidly as feasible. For example, if the time out of reactor increases from 9 to 33 months. the requirement for imported uranium rises by 75%. International collaboration continues to play a large part in the UK R and D programme and there is an active exchange between the UK and all those Countries with operating fast reactors. Possibilities for international collaboration in at least the early stages of a commercial programme of fast reactors are currently being considered by the government